When Height and Width properties are explicitly set on an element, these measurements take layout precedent and cancel the regular effects of setting this property to Stretch.

VerticalAlignment is the Microsoft .NET property accessor for what is in reality a dependency property. This particular dependency property quite frequently has its apparent "default" value set differently in derived element classes, particularly controls. This generally occurs in one of two ways: the dependency property is re-registered to a particular derived class, but with different metadata for setting its defaults; or there is a default style being applied that sets that dependency property value differently. For example, the apparent "default" of VerticalAlignment for a ComboBoxItem control will be Center, even though ComboBoxItem inherits VerticalAlignment direct from FrameworkElement. This is because that value was reset within the default style of ComboBoxItem, within the style's control template.

Canvas does not use VerticalAlignment when composing layout, because Canvas is based on absolute positioning.